1. Field of the Invention
The present invention relates to a sheet stitching apparatus which cuts a wire reeled out from a wire reel only a predetermined length, bends the cut wire into a U-shape, drives the wire into a set of sheets, bends both ends of the U-shaped wire so as to stitch the set of sheets, and more particularly, to detection of abnormal motion of the sheet stitching apparatus.
2. Description of the Related Art
The sheet stitching apparatus is arranged in a saddle stitch book-binding apparatus used in conjunction with a sheet collator. FIG. 5 is a schematic diagram of such a saddle stitch book-binding apparatus. In FIG. 5, a reference number 31 represents the sheet collator, a reference number 32 represents a stitching head of the sheet stitching apparatus, a reference number 33 represents a clincher of the sheet stitching apparatus, a reference number 34 represents a wire reel, a reference number 35 represents a plate spring type wire guide, a reference number 36 represents a folding knife of a sheet folder, a reference number 37 represents a folding roller of the sheet folder, a reference number 38 represents a cutter of a guillotine cutter, a reference number 39 represents a delivery roller, and reference numbers 40a and 40b represent discharge trays.
A set of sheets collated by the sheet collator 31 is supplied to the sheet stitching apparatus. The set of sheets is positioned at a stitching position, and a center line of the set of sheets is aligned with the stitching head 32 and the clincher 33. The stitching head 32 reels out a wire from the wire reel 34 via the wire guide 35, the stitching head 32 cuts the wire only a predetermined length, bends the cut wire into a U-shape and drives the U-shaped wire into the set of sheets. Simultaneously when the wire is driven, both ends of the U-shaped wire passed through the set of sheets are bent inward by the clincher 33, and the set of sheets is stitched. The stitched set of sheets is fed to a folding position, and folded into two along a stitching portion by the folding knife 36 and the folding roller 37. The folded set of sheets is fed to a cutting position, is trimmed by the cutter 38 at its front edge portion, and discharged into the discharge tray 40a or the discharge tray 40b via the delivery roller 39.
In the conventional sheet stitching apparatus, even when a trouble occurs in supply of the wire to the stitching head 32, the stitching head 32 keeps operating and a sheet stitching error is caused in some cases. In such a case, if the apparatus is not stopped immediately, detective products not-stitched are discharged one after another from the book-binding apparatus.
Hence, there is proposed a book-binding apparatus in which a detector for detection of a wire is arranged in midstream of a wire feed path from the wire reel to the stitching head, and when a wire is not detected, the sheet stitching apparatus is stopped (see Japanese Laid-Open Patent Publication No. 2005-74866).
According to this configuration, the detector can detect an error when a wire to be supplied to the stitching head runs out or a wire is cut in midstream of the wire feed path, but when the wire feed path clogs up or a wire becomes entangled or the stitching head does not operate normally, an error can not be detected, so that there is a problem that defective products are discharged one after another due to the abnormal operation of the sheet stitching apparatus.
To solve this problem, there is proposed another sheet stitching apparatus capable of detecting an error in wire feed operation instead of detecting a wire itself (see Japanese Laid-Open Patent Publication No. 2007-307892). FIG. 4 is an elevational view of a conventional sheet stitching apparatus. Referring to FIG. 4, the sheet stitching apparatus comprises a clincher 1 mounted on a frame (not shown), and a stitching head 2 arranged oppositely to the clincher 1 for reciprocal vertical movement between a standby position in which it is upwardly separated from the clincher 1 and a stitching position in which it abuts to the clincher 1. Although it is not illustrated in the drawing, the stitching head 2 is guided by a guide member mounted on the frame so as to be moved vertically, and is moved by a drive mechanism.
A wire insertion pipe 3 is mounted on an upper end of the stitching head 2 and extends upward from the stitching head 2. A base end 4b of the wire guide 4 consisting of a thin and long plate spring is fixed to an upper end of the wire insertion pipe 3.
A wire reel 5 is rotatably supported by a frame F. The wire reel 5 is located below a tip end 4a of the wire guide 4 and a side 5a thereof is arranged oppositely to one side 4c of the wire guide 4.
The wire guide 4 is bent in such a manner that the tip end 4a of the wire guide 4 is directed toward the wire reel 5 and the one side 4c is medially located, and at the same time, a wire W reeled out from the wire reel 5 is guided along the other side 4d of the wire guide 4, led through the wire insertion pipe 3, and supplied to the stitching head 2.
When the stitching head 2 is in the standby position, the stitching head 2 pulls in a wire W only a predetermined length and cuts the wire W, and while the stitching head 2 lowers from the standby position, the stitching head 2 bends the cut wire W into a U-shape, and when the stitching head 2 reaches the stitching position, the stitching head 2 drives the U-shape wire into the set of sheets S and the clincher 1 bends both ends of the U-shape wire.
One end of a thin and long support plate 6 is fixed to an upper end of the wire insertion pipe 3, and the support plate 6 is arranged oppositely to the one side 4c of the wire guide 4 at its one side 6a. The other end of the support plate 6 is provided with a proximity sensor 7 at its one side 6a. 
When the stitching head 2 performs pull-in operation of wire, first, the wire W is pulled in the stitching head 2, while the wire reel 5 is not rotated, so that the tension applied to the wire W is increased, and thereby the wire guide 4 is bent. Consequently, the wire guide 4 approaches the proximity sensor 7 and the proximity sensor 7 detects the wire guide 4. Thereafter, the wire reel 5 is rotated by the restoring force of the wire guide 4 so as to reel the wire W out, so that the wire guide 4 returns to its original position. Consequently, the wire guide 4 gets away from the proximity sensor 7 and the proximity sensor 7 does not detect the wire guide 4.
The proximity sensor 7 detects the change of position of the wire guide 4 effected by the pull-in operation of wire W by the stitching head 2, whereby the timing of the change of position of the wire guide 4 is compared with the timing of stitching operation of the stitching head 2 and an error of wire feed operation is detected.
In the sheet stitching apparatus, however, when the remaining amount of wire of the wire reel 5 is large, the wire guide 4 is largely bent due to large tension applied to the wire W, the initial position of the wire guide 4 is close to the proximity sensor 7 (position (I) in FIG. 4), and as the remaining amount of wire of the wire reel 5 is reduced, since tension applied to the wire W is reduced, the degree of bending of the wire guide is reduced, and the initial position of the wire guide 4 gets away from the proximity sensor 7 (position (II) in FIG. 4). When the initial position of the wire guide 4 is largely changed, there occurs a problem that the change of position of the wire guide 4 due to the motion of the stitching head 2 can not be detected precisely.